NOAA/WDS Paleoclimatology - Intensification of southwestern Indonesian rainfall over the past millennium

STUDY NOTES: Samples for dDwax analysis were taken at an average resolution of 8.5years (ranging approximately 3 to 25years). One hundred seventy sediment samples were freeze-dried, homogenized, and extracted using a Dionex Accelerated Solvent Extractor 350 to yield the soluble lipid fraction. Fatty acids were then purified according to previously described methods [Konecky et al., 2011]. dD was measured on the C28 n-alkanoic acid, the dominant homologue in all samples, using gas chromatography- pyrolysis-isotope ratio-mass spectrometry. Samples were randomized and run in duplicate, except for a subset of 18 samples that were run in triplicate. The pooled standard deviation of triplicate samples was 1.08%, and the 1-s error on a synthetic fatty acid methyl ester standard run between every six replicates was 2.5%. dDwax values are reported relative to Vienna Standard Mean Ocean Water. Leaf wax delta-D(C28 n-alkanoic acid) from Lake Lading, East Java, Indonesia. ADDITIONAL REFERENCE FOR FATTY ACID PURIFICATION: Konecky, B. L., Russell, J. M., Johnson, T. C., Brown, E. T., Berke, M. A., Werne, J. P., & Huang, Y. (2011). Atmospheric circulation patterns during late Pleistocene climate changes at Lake Malawi, Africa. Earth and Planetary Science Letters, 312(3), 318–326.
ABSTRACT SUPPLIED BY ORIGINATOR: Modern precipitation in Indonesia is strongly correlated to variations in the Asian/Australasian monsoons, the Walker circulation, and migrations of the Intertropical Convergence Zone (ITCZ), but controls on multi-decadal to millennial rainfall variations are less clear. We present a new, high-resolution, precipitation proxy reconstruction from Lake Lading (8S, 113E), Java, from 850 C.E. to present, based on the dD of terrestrial plant waxes. We find that rainfall has steadily increased in Java over the past millennium. This increase persists into the 20th century, despite evidence from other tropical proxy records for a northward ITCZ migration during the last two centuries, which should introduce drier conditions to Java. Aspects of this long-term increase in rainfall resemble records from the northern hemisphere, tropical Indo-Pacific, suggesting that strengthening Walker circulation played an important role in this long-term increase in rainfall and decrease in the dD of precipitation, while ITCZ variations may have been important to climate variations on multi-decadal to centennial timescales.